1. Field of the Invention
Embodiments of the invention generally relate to the field of semiconductor manufacturing processes and devices, more particular, to methods of depositing silicon-containing films forming semiconductor devices.
2. Description of the Related Art
As smaller transistors are manufactured, ultra shallow source/drain junctions are becoming more challenging to produce. According to the International Technology Roadmap for Semiconductors (ITRS), junction depth is required to be less than 30 nm for sub-100 nm CMOS (complementary metal-oxide semiconductor) devices. Conventional doping by implantation and annealing is less effective as the junction depth approaches 10 nm. Doping by implantation requires a post-annealing process in order to activate dopants and post-annealing causes enhanced dopant diffusion into layers.
Recently, heavily-doped (about >1019 atoms/cm3), selective SiGe epitaxy has become a useful material to deposit during formation of elevated source/drain and source/drain extension features. Source/drain extension features are manufactured by etching silicon to make a recessed source/drain feature and subsequently filling the etched surface with a selectively grown SiGe epilayer. Selective epitaxy permits near complete dopant activation with in-situ doping, so that the post annealing process is omitted. Therefore, junction depth can be defined accurately by silicon etching and selective epitaxy. On the other hand, the ultra shallow source/drain junction inevitably results in increased series resistance. Also, junction consumption during silicide formation increases the series resistance even further. In order to compensate for junction consumption, an elevated source/drain is epitaxially and selectively grown on the junction.
Selective Si epitaxial deposition and SiGe epitaxial deposition permits growth of epilayers on Si moats with no growth on dielectric areas. Selective epitaxy can be used in semiconductor devices, such as within elevated source/drains, source/drain extensions, contact plugs, and base layer deposition of bipolar devices. Generally, a selective epitaxy process involves two reactions: deposition and etching. They occur simultaneously with relatively different reaction rates on Si and on dielectric surface. A selective process window results in deposition only on Si surfaces by changing the concentration of an etchant gas (e.g., HCl). A popular process to perform selective, epitaxy deposition is to use dichlorosilane (SiH2Cl2) as a silicon source, germane (GeH4) as a germanium source, HCl as an etchant to provide selectivity during the deposition and hydrogen (H2) as a carrier gas.
Although SiGe epitaxial deposition is suitable for small dimensions, this approach does not readily prepare doped SiGe, since the dopants react with HCl. The process development of heavily boron doped (e.g., higher than 5×1019 cm−3) selective SiGe epitaxy is a much more complicated task because boron doping makes the process window for selective deposition narrow. Generally, when more boron concentration (e.g., B2H6) is added to the flow, a higher HCl concentration is necessary to achieve selectivity due to the increase growth rate of deposited film(s) on any dielectric areas. This higher HCl flow rate proportionally reduces boron incorporation into the epilayers presumably because the B—Cl bond is stronger than Ge—Cl and Si—Cl bonds.
Therefore, there is a need to have a process for selectively and epitaxially depositing silicon and silicon compounds with an enriched dopant concentration. Furthermore, the process must maintain a high growth of the deposited material. Also, the process must have less dependency on germanium and boron concentrations in the silicon compound in relation to an etchant flow rate.